Lately, rubbers used for tires must have reduced hysteresis loss values in order to reduce energy consumption. For that purpose, natural rubber, polyisoprene rubber, and polybutadiene rubbers (BR) are used because they have low hysteresis loss values.
Some synthetic polymers with very low hysteresis loss values are prepared by coupling after being formed by polymerization using organic lithium compounds, the coupling being carried out with halogenated tin compounds (JP-A-57-55912, etc.). These polymers have good properties, in particular, reduced energy consumption.
Another method for lowering the hysteresis loss value includes the use of polymers having amine group at the end of the chains (JP-A-50-79590, JP-A-52-22484, etc.). In this process, initiators, such as amide compounds of alkali metals or cyclic lithium imide compounds, are prepared separately before use. In these process, hysteresis loss values are lowered by introducing tin atoms in the polymers thorough coupling.
However, the methods described above require a coupling step after polymerization, which prevents continuous polymerization, therefore, reducing productivity.